Does A Fiance Have Legal Claim To An Estate?

This is being posted from a throwaway account for privacy reasons.

Let's say you are a single man, never married, with no bio children, late 70's, in declining health. You've recently become engaged to a woman (early 70's) and she is moving into your home. (Side note: you actually have no intention of marrying this person, you just don't want to spend another winter alone and you get along well enough.)

Your biggest asset is your home and you own it outright. It's likely worth 400-500k now. You have a will that leaves everything to your niece, nephew, and the children you helped raise from your last long-term relationship that lasted 20 years.

Let's say you pass away in the next 5 years. Does the live-in fiance have a claim to your estate by virtue of being engaged to you? How would you protect your assets from the fiance if they did have a claim? Any other advice you could give to someone in this situation?

I'm writing this as if a hypothetical but it's obviously a real situation. This new fiance has thrown a few red flags. For starters: he asked her to move in with him and she insisted that she wouldn't "shack-up" without being engaged first. So he said "Fine, we're engaged." They've known each other for about a year.